Could the future of a salt marsh be hidden in the health of its microbes? Scientists say yes.

Salt marshes play key roles in reducing the effects of urbanization and climate change. Marshes absorb carbon dioxide from the atmosphere, and their microbes break down carbon.

That’s why researchers are working to find out how these vital ecosystems tick.

Jennifer Bowen of Northeastern University and colleagues have studied microbes in the sediments of salt marshes in the National Science Foundation (NSF) Plum Island Ecosystems Long-Term Ecological Research (LTER) site in northeastern Massachusetts.

They’re working to discover how the marsh — and the microbes in it — change over time when outside influences, such as nitrogen, are introduced to the ecosystem.

“A lot of the ecological services salt marshes provide are facilitated by microbes,” Bowen said. “They’re involved in the carbon cycle and the nitrogen cycle, and they remove nutrient pollution through their metabolic processes.”

Dormant microbes

In a new paper published in the journal Nature Communications, Bowen and her Northeastern colleague Patrick Kearns, who is first author of the paper, along with researchers at the Marine Biological Laboratory and Woods Hole Oceanographic Institution, set out to discover what would happen to microbes in salt marshes if specific nutrients were added to the environment — through urbanization and climate change, for example.

Adding nutrients like nitrogen produced no change in the types of bacteria present in the salt marsh — at least, temporarily. But over time, a large number of the microbes became dormant.

“It’s kind of like a bear going into hibernation,” Bowen said. “These dormant bacteria are in a low metabolic state. They just bide their time until environmental conditions return that are suitable for them.”

When the microbes go dormant, they don’t contribute to the critical ecosystem services that make salt marshes important.

Human-salt marsh interactions

“This study shows that human activities are affecting bacteria essential to salt marshes in ways we never suspected,” said Matt Kane, program director in the NSF Division of Environmental Biology, which co-funded the research with NSF’s Division of Ocean Sciences. “Coastal salt marshes provide many benefits — supporting diverse wildlife, helping to reduce pollution, and protecting us from flooding.”

What happens to salt marshes and their bacteria, Kane explained, ripples into human lives.

The study’s results help explain why salt marshes contain so much microbial diversity. One group of microbes is specialized for a specific set of conditions, while another is linked with others. As the environment changes, different bacteria take advantage of the conditions that are most suitable to them.

“These investigators have made an important discovery about the resilience of microbial communities in salt marsh ecosystems,” said David Garrison, program officer in NSF’s Ocean Sciences Division.

A salt marsh, the researchers say, is a constant balancing act.

“If we see an increase in the abundance of bacteria that are able to decompose the marsh, we also see an increase in bacteria that can help fix carbon,” Bowen said. “If a marsh is failing, there is no way to restore the microbes. But what can be created is an environment that will help these microbes thrive.”

Add fertilizer to your garden and your plants will probably grow bigger and taller. Add fertilizer to a salt marsh and the plants may not get any bigger. That’s according to a new study led by Dr. David Samuel Johnson of William & Mary’s Virginia Institute of Marine Science.

Salt marshes are intertidal grasslands that grow at the interface between land and sea. These ecosystems can receive excess concentrations of nutrients such as nitrogen from wastewater and runoff of agricultural fertilizer.This “eutrophication” affects coastal waters and estuaries worldwide and can lead to fish kills, harmful algal blooms, and areas of low oxygen. Johnson and his team wanted to know how eutrophication impacted salt marshes.

To do so, the team conducted an unprecedented experiment and flooded football-fields worth of salt marsh in northeastern Massachusetts with fertilizer-rich water for almost a decade. Scott Warren, a professor at Connecticut College and study co-author who has studied salt marshes for four decades, says “When we were able to mimic a eutrophied estuary at an ecosystem scale—quite a challenge I must add—we found that salt marshes did not respond as you might have predicted from fertilization experiments done over the past half a century or so.”

Despite the abundant supply of nitrogen, a key plant nutrient, plants in the fertilized marshes didn’t grow much bigger than those in unfertilized marshes. “We were surprised at the mild responses, even after almost a decade of fertilization,” says Johnson. Earlier salt marsh studies reported plants growing larger in response to adding fertilizer. Previous studies also found that fertilizer changed species composition, causing some species to outcompete others. “The species composition didn’t budge during the entire experiment,” Johnson says.

One reason the team’s results differed from previous studies may be their choice of fertilizer. “We used nitrate fertilizer, which is the most common form of nitrogen in eutrophied estuaries,” says Johnson. “Much of the previous work used ammonium fertilizer. Those studies had different questions than ours; they weren’t specifically looking to understand eutrophication.” Wetland plants prefer ammonium to nitrate because it takes less energy to process, so bigger plants with application of ammonium would not be unexpected.

Another reason the plants may not have responded strongly was the way the fertilizer was delivered—with flooding tidal water, which meant that less fertilizer reached the plants compared to previous studies that had added fertilizer directly to the marsh surface.

The mild response of plants doesn’t mean that salt marshes are safe from eutrophication, however. Johnson notes that when it comes to understanding eutrophication’s impact on salt marshes, the answer may lie beneath the surface. In an earlier paper from the same field study, published in Nature, the research team found that fertilizer treatments caused the marsh edges to collapse and erode away. Again, this is opposite of what they had predicted. “We hypothesized that the grass would grow taller, which would trap more sediment and help the marsh grow,” says Johnson. Instead they found that plants in fertilized marshes had fewer roots and rhizomes than those in non-fertilized ones, which may have contributed to the collapse.

The team’s research results have important implications for the management and care of salt marshes. These critically important coastal resources are thought to be “nutrient sponges” that soak up excess nitrogen to help prevent dead zones and fish kills. One way they can do so is by putting the nitrogen into bigger plants. Since the plants in the current study didn’t grow bigger, it limited the marsh’s ability to absorb excess nitrogen.

Johnson adds, “Our work underscores that we can’t simply rely on salt marshes to clean up nutrient pollution. We need to do a better job at keeping nutrients out of the water in the first place.”

Friday afternoon, and five marsh-logged REUs eagerly stuffed clothes into bags, piled into cars and headed south. After a long week, we were more than ready for time off. Three hours later, after driving like salmon through Boston traffic, we arrived at the Cape and hit the town for some shopping and seafood. Our rag-tag group was prepping for what promised to be a wild weekend. But by wild, I mean there were a lot of people. And by people I mean scientists. And by scientists, I mean the speakers and attendees for the Celebrating Discovery conference at the Marine Biological Laboratory of Woods Hole.

“A Summer Camp for Scientists”

Woods Hole, MA has an international reputation as the hub for marine science research. Along a half-kilometer long road, the Marine Biological Laboratory (MBL), Woods Hole Oceanographic Institute (WHOI), and the National Oceanic and Atmospheric Administration (NOAA) all have prestigious research facilities. A mere five minute walk and I could have caught flies – my jaw dropped, and never have I felt like such a kid in a candy shop. Within the greater Woods Hole area, the United States Geological Survey, the National Academy of Sciences, and Semester at Sea also have facilities.

The coastline is peppered with hulking research vessels, docked for the summertime. Quaint coffee shops and restaurants attract tourists and scientists alike, where it is not uncommon to overhear sincere discussions about the future of bioinformatics. I was thrilled to be in an area associated with such prestige and history (MBL has produced over 50 Nobel laureates), and even more awe-struck that I somehow fit into the giant cog of this machine.

WHOI’s Knorr. Fun fact–it’s the ship that found the wreck of the Titanic

The Celebrating Discovery conference took the form of “plenary sessions”, meaning a series of speakers would give talks within the same general topic. Speakers from UC Berkeley, WHOI, Harvard, Duke University, Brown, Dartmouth, the Amazon Environmental Research Institute, Argonne Laboratories, the Smithsonian, Howard Hughes Medical Institute and more, presented on everything from eco-evolutionary biology to computational modelling and medical breakthroughs in tissue regeneration. MBL is officially affiliated with Brown University and the University of Chicago, and collaborates with other universities and laboratories across the world. By simply walking into the auditorium for a lecture, you felt smarter. Some of the most brilliant minds in the marine sciences were in the room. While the weekend may not have been “wild” by Cape Cod’s standards, it was an intellectually stimulating and highly social event.

Scientists are often portrayed as socially awkward, brooding, and plain weird; in the digital age of professional-networking platforms (e.g LinkedIn and ResearchGate) and email-related frenzy, it would be more than easy for scientists to entirely block out physical connection with the outside world. Publications are the primary way that the scientific community connects with one another. Yet, it is during conferences that we make the most interdisciplinary connections. Conferences provide dedicated venues and forums for scientists of all specialties to meet and learn from one another. The standing joke is that MBL is a summer camp for scientists, as we much prefer sitting on beaches in deep conversation than locked away in a cold dark basement lab. (Beach time was existent but unfortunately minimal). By the end of the weekend, each of us had further honed our interests and met someone who was driving scientific inquiry in their field. It opened our eyes to the deeply collaborative nature of the MBL, and showed that despite the name, MBL does not restrict its limitless ideas to the seas.

Selfie in between plenary sessions. “It’s for the blog”

MBL’s remarkable collaboration with numerous institutions is further highlighted in its equal success in communicating its research. While conferences are wonderful places for scientists to share new ideas, it is meaningless unless conveyed to policy-makers, medical experts, and the general public. As one example, MBL sponsors Friday evening lectures throughout the summer that draw crowds to fill two auditoriums, with internationally known speakers. The lecture is followed by a beautiful reception, where people of all backgrounds can mingle. Local outreach is equally as important; non-scientific residents can appreciate the importance of those hulking research vessels that block their view of the ocean. Our own blog gives the TIDE project a digital presence to communicate to public the imperative nature of our own work, and even attract future researchers. (It also provides excellent writing practice for the interns – that’s me!)

When communication of new ideas and questions is effective, it can change the people’s perception of environmental problems. Communication comes in a plethora of forms, from books that start a green revolution, to 140 character tweets. We cannot keep our ideas to ourselves; science is worth nothing if no one else knows. MBL’s weekend of discovery was about asking relevant scientific questions to reach novel intellectual destinations and foster a diverse intellectual community. The depth and breadth of researchers that are attracted to Woods Hole is already staggering, but the MBL is pushing the frontier of discovery.

If ideas are truly the currency of the 21st century, then these giddy summer-campers struck gold.

We made it to the beach! (From left to right: Frankie Leech, Bryn Mawr; Nathalie Moore, College of William and Mary; Kassandra Baron, Washington and Jefferson; Caitlin Bauer, Bryn Mawr)

Nathalie Moore is a rising junior at the College of William and Mary. She is a double major in Biology and Environmental Science, and her summer research for the MBL focuses on salt marsh creek bank degradation and foraging success of a top predator, F. heteroclitus. She will be presenting her work on Austral invasion and fire ecology at the 100th Meeting of the Ecological Society of America in Baltimore, MD on August 13th.

Kass installs her mesocosm testing the effects of Melampus snails on cordgrass decomposition

Time is flying by and we are already halfway through the field season! I am Kassandra Baron and I am an undergraduate student from Washington & Jefferson College studying Biology. Here at the Marshview field station I work as a research undergraduate student. This summer I am working on the TIDE project as well as carrying out several experiments with an invertebrate commonly found on the high marsh, Melampus.

Melampus bidentatus, the coffee bean snail

Melampus bidentatus, commonly known as the Coffee Bean snail, is a terrestrial air-breathing snail in the family Ellobiidae. This species is relatively small, averaging 9 to 12 mm when fully grown. As a detritivore located on the high marsh, Melampus commonly feeds on Spartina patens and the algae that grows on the stems of these plants. The majority of my project is researching the effects of Melampus density on Spartina patens litter processing. While exploring density effect, I am also pursuing the question on whether or not there is a fertilizer effect. In both of my experiments we are using dead Spartina patens from Sweeney and West creeks and Melampus. Sweeney creek serves as our enriched creek and West creek is used as our reference. By using these two different creeks, we can compare the effect of Melampus on mass loss.

Caging a pre-weighed amount of dead cordgrass and a particular number of snails will help reveal how coffee bean snails contribute to cyclical plant decomposition in the marsh

To better understand whether or not Melampus increases the decomposition rate of Spartina litter that has been nutrient enriched, two experiments were set up. One experiment takes into consideration natural environmental factors and Melampus in its natural habitat. In this experiment, I used decomposition bags made of window screen and placed a known amount of dead Spartina patens and different densities of snails in each bag. These bags were then deployed out in the field at both creeks each containing litter from that creek. For the second experiment, I set up petri dishes. Half of these dishes contained litter from Sweeney creek and the other half West. Each dish had a known mass of detritus and a random density, or number, of Melampus individuals.

At the end of the field season, roughly 8 weeks from now, I will be measuring the mass loss, nitrogen content, phenolic content, particle size, and snail growth for both experiments. All together I hope to gain a better understanding of the importance of this snail on decomposition and determine if nitrogen enrichment and density play a role in the process of decomposition.

My name is Drew Collins, and I’m a rising junior at the University of New England studying Marine Biology. I’m one of the REU (Research Experience for Undergraduates) Interns working out of the Marshview Farm field station on the TIDE project.

As part of the REU program, interns must plan, orchestrate, and present the findings of a scientific study of their choosing (all within ten weeks!). We are not alone in this process however, as we have an incredible network of scientists working out of Marshview. The TIDE PIs (Principal Investigators, lead researchers) have been invaluable, giving us an endless stream of knowledge and advice they have gained through their many research projects and scientific endeavors. I know this advice will continue to help and guide me long after this summer is over. The RAs (research assistants) provide both advice and lend a hand with the lab work and fieldwork these projects require. In addition, all the REUs help each other, surveying creeks, gathering and counting snails, measuring gr ass clippings, and labeling everything.

Nathalie taking geomorphic measurements on one study creek such as point vegetation cover, bank crack widths, and creek depth.

My project is a joint project with Nathalie Moore. Together we are studying how the changing landscape of the marsh creeks is affecting mummichogs’ (a species of small fish that lives in the marsh) access to their invertebrate prey in the upper marsh. In order to get a large sample size of creeks, Nathalie and I have had to travel all over the Rowley and Ipswich salt marshes, exploring creeks not often visited. Once we had chosen and surveyed our creeks, we now must take measurements on the fish and the invertebrates at each creek, so we can see what kind of relationship there is between the landscape of the creek, the types and quantity of invertebrates, and the size, mass and behavior of the mummichogs living there.

Nathalie uses an old downed telephone pole to cross a ‘mosquito ditch’ while working at Metcalf creek

This internship has been a really exciting opportunity for me specifically, because the areas we study are practically in my backyard. I live just 10 minutes from Marshview, and I grew up here on the Great Marsh. To be able to do real science on these salt marshes, which have always held a special place in my heart has been a truly magical experience.

Hello TIDE enthusiasts! We, Caitlin and Frankie, are excited to be writing the first blog post of the field season. We are rising seniors at Bryn Mawr College. While Caitlin is a seasoned marsh expeditionist returning for her third summer, Frankie is excited to start her first summer here at TIDE. The marsh has been treating us well these first few weeks, and has welcomed us with a mixture of cold/rainy and hot/sunny days.

Not even cold and rainy weather can keep the REUs away from tank fills at Sweeney Creek

This summer, we will both continue to work with the plants that inhabit the Plum Island Marsh here at TIDE. Our focus is to compare the phenology of Tall Form Spartina alterniflora (TSA) to genetic analysis conducted last year. We will continue to take clip plots of the five main marsh plants, TSA, Short Form Spartina alterniflora (SSA), Distichlis spicata (DS), and Spartina patens (SP) in order to determine changes in plant morphology and density between the fertilized and unfertilized creeks. We will also measure gas fluxes, including methane, CO2 and water vapor, to investigate differences in plant physiology across the long term fertilized Sweeney Creek and the unfertilized West Creek.

During our short time here, we have also had the opportunity to assist with other projects, as well as attend and present a poster at the New England Botanical Society’s 120th anniversary conference. We had a great time there and were excited to be able to visit another one of the Seven Sister’s, Smith College, who hosted the conference. We look forward to collaborate with the other REUs and further develop our understanding of essential marsh systems. Flume Netting is the next big project coming up this week, and we have begun to move the nets to more appropriate locations on the marsh.

Caitlin and Frankie measure TSA in their flux collars at Sweeney Creek. Height measurements will be taken twice each month in all of the collars at both Sweeney and West.

Marshes are quiet, unassuming ecosystems that do a lot for us. They provide protection from storms, they produce animals that we like to eat or watch, and they give us wonderful places to look out upon while watching the sunrise (or set on the West Coast). WCAI, the Cape and Islands NPR station, highlighted salt marshes last week in their Living Lab segment. Linda Deegan, the lead Principal Investigator was a part of the discussion. If you want to learn about salt marshes, this is a good place to start so give a listen.